Objectives of this project are (1) to establish and define a cell culture transformation system for identification of carcinogenic agents and humans at high risk for cancer; (2) to develop human cell transformation systems, with particular emphasis on epithelial cells, in order to study host factors regulating cell transformation and the mechanisms of carcinogenesis by chemicals, viruses, hormones and x-irradiation; and (3) to isolate and characterize oncogenes from human tumors. In line with these objectives, we have (1) established a nontumorigenic human epidermal keratinocyte line immortalized by transfection with pSV3-neo; (2) demonstrated malignant transformation of human epidermal keratinocytes by the combined action of SV40 T antigens and K-MSV; (3) demonstrated enhanced G-2 chromatid radiosensitivity in continuous cell lines established by infection with adeno 12-SV40 or transfection with pSV3-neo; (4) established human epidermal keratinocyte lines expressing SV40 T antigens, malignantly transformed with chemicals for detection of new human cellular oncogenes; (5) demonstrated that human epidermal keratinocytes retain radiation resistance following in vitro immortalization and malignant transformation; and (6) demonstrated activation of a cellular transforming oncogene, H-ras, in the human 312H cell line transformed with the chemical carcinogen, 3- methylcholanthrene.